There are numerous designs for acoustical stringed instruments that may be plucked or bowed. Conventionally these instruments comprise a hollow body having one or more openings serving as sound holes. The strings are tensioned over the hollow body such that the hollow body forms a sounding board for vibrations of the strings when plucked or bowed. In many cases the sound intensity produced by an acoustical stringed instrument is not enough when the instrument is used in a large spaces. Therefore, there are acoustical instruments provided with resonators or diaphragms to intensify the sound produced by the instrument when plucked or bowed. These kinds of instruments are described in, for example, U.S. Pat. Nos. 1,762,617; 1,741,453; and 1,872,633. In the instruments described in the mentioned patents above, the vibration of the strings is transferred to the diaphragm that enhances the sound by vibrating.
One of the disadvantages associated with the above arrangements is that the diaphragms have to support the downward pressure of the strings on a bridge provided on the top of the hollow body of the instrument. Therefore, the diaphragms have to be made considerably rigid, and of materials which do not creep under load. The movability of such diaphragms is limited and therefore the radiation of sound is also limited. This limitation is accentuated at low frequencies, which needs large movement of the diaphragm. The need of a large displacement of air is also underlined by the relative insensitivity of the human ear at low frequencies. Furthermore, in the old designs with resonators the rear side of the diaphragm is in contact with the inner cavity of the instrument body. The sound is then radiated through openings in the body. The cavity of undefined hollow shape cannot enhance or amplify the sound, instead it dampens it.